Devices having a retractable sheath associated with a catheter are used to treat a variety of conditions using endoluminal methods instead of open surgical procedures. For example, angioplasty and stent implantation procedures are often used to treat atherosclerotic disease or other occlusive conditions in blood vessels, such as the coronary and carotid arteries. During angioplasty, for example, a catheter having an uninflated balloon on its distal end is percutaneously introduced into a patient's vasculature and advanced to a target treatment location, such as a stenosis within a blood vessel. Once the balloon is properly placed across the stenosis, the balloon is inflated to enlarge the lumen at the location. The balloon is then deflated, the inflation/deflation procedure may be repeated, and then the catheter is then withdrawn from the patient's body.
Often in conjunction with angioplasty, a stent or other tubular prosthesis may be implanted within a stenosis to scaffold the location and prevent it from contracting or otherwise becoming obstructed again. The stent, in a contracted condition, is generally placed upon a catheter, possibly over a balloon. The catheter is advanced to the target stenosis until the stent is adjacent to the location, and then the stent is deployed and substantially anchored at the location. The stent may be biased to expand to an enlarged condition and/or may be expanded with the aid of a balloon, as with plastically deformable stents, until the stent substantially engages the wall of the vessel. Once the stent is implanted, the delivery catheter is withdrawn from the patient.
Similarly for ablation procedures and the like, a catheter including an array of electrodes, for example, on an expandable basket assembly, may be provided. The device may be introduced into a body lumen, for example through the patient's vasculature into the heart, to treat conditions, such as heart arrhythmia.
With any of these systems, a sheath may be provided over the distal end of the catheter to protect the components on the distal end, such as a balloon, a stent, an array of electrodes, and the like. The sheath may be advanced distally over the proximal end of the catheter until it covers the distal end and its components, or, alternatively, the distal end of the catheter may be introduced into the sheath, and advanced until it is proximate the distal end of the sheath. Once the distal end of the catheter is properly positioned at a desired location within a body lumen, the sheath may be retracted to expose the distal end of the catheter. After treatment, the sheath may be advanced back over the distal end of the catheter, and the entire device withdrawn from the patient.
To cause the sheath to retract, the proximal end of the sheath outside the patient may simply be pulled while holding the catheter in a fixed position. This, however, may not provide very precise control of the retraction of the sheath. To provide improved control, handle devices have been proposed that include a wheel and screw mechanism. A wheel extending around the circumference of the handle is coupled to a screw mechanism engaging the sheath and the catheter. As the wheel is rotated about the longitudinal axis of the handle, the screw mechanism directs the sheath axially with respect to the catheter.
With such devices, however, it may be difficult to remember which direction, i.e., clockwise or counterclockwise, is appropriate either to retract or advance the sheath with respect to the catheter. This may be particularly important when immediate action is necessary because of a complication during a procedure. Moreover, in such devices, it is possible to advance the sheath in the distal direction during and after deployment of the device, such as a stent, on the distal end of the catheter. This distal movement may result in the improper placement and unwanted movement of the deployed device. This distal movement of the sheath is particularly problematic in the deployment of stents or other tubular prostheses. It is preferred that a catheter-sheath system have only unidirectional motion, i.e., only permit retraction of the sheath in the proximal direction.
Another disadvantage in current screw-type devices is that the devices are often complicated, including many parts which may be difficult to assemble and/or expensive to make.
Accordingly, there is a need for more intuitive, more simple, and/or less expensive devices for controlling catheter-sheath systems.